The present invention relates to a system for converting information in the form of an AC frequency to corresponding digital data suitable for processing by a digital computer. Such systems enjoy a wide variety of applications and are particularly useful for generating digital signals representative of the angular velocity of a rotating mass. Such digital signals are widely used in various control and measurement systems such as in digital controls for aircraft engines.
Prior art systems have used various pulse counting schemes which count at a fixed rate throughout the duration of the period or half period of the AC signal. Such techniques have been found to be inaccurate for applications in which the information of interest is contained at higher frequencies since these systems produce a digital number which has least resolution at such higher frequencies. Other prior art systems have used converters to convert the AC frequency to a DC analog voltage and thereafter an analog to digital converter to convert the analog signal to a digital voltage. These systems, however, also produce errors in the digital signal due to the drift of the various analog components used.